JP2600725B2 - Data demodulation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a data demodulation circuit suitable for application to an optical disk reproducing apparatus for reproducing an optical disk on which 8-bit data is recorded by so-called 4/15 modulation. About.

[Summary of the Invention]

The present invention relates to a data demodulation circuit for obtaining 8-bit data from a reproduction signal of a recording medium in which 8-bit data is recorded by so-called 4/15 modulation, and corresponds to each bit position of 15-bit data. `` 0
A pattern of “0” is detected, and the operation of the differential detection means is controlled based on the detection output, and the “0”
High level "1" at the bit position corresponding to the pattern "0"
Are prevented from being output, thereby preventing erroneous data demodulation.

[Conventional technology]

2. Description of the Related Art Conventionally, erasable and re-recordable optical disks are known. An example of such an optical disk is a magneto-optical disk. The magneto-optical disk records data according to the direction of magnetization. That is, in a magneto-optical disk, a perpendicular magnetization film whose magnetization is oriented perpendicular to the disk surface is used as a recording medium. This recording medium has a coercive force at room temperature and the direction of magnetization does not change. When the recording medium is irradiated with a laser beam, the temperature of that portion rises sharply, and when it reaches the Curie temperature, the holding power decreases. For this reason, when a weak magnetic field is given from the outside and a laser beam is irradiated on the magneto-optical disk, the temperature of that portion sharply rises and the direction of magnetization is reversed. As a result, a magnetization reversal pattern is formed, and data is written. Data reading is performed by irradiating a laser beam to the magneto-optical disk and detecting the rotation of the polarization plane of the reflected light.

As a modulation method for recording data on such a magneto-optical disk, 4/15 (4 out of 15) modulation has been proposed. In the 4/15 modulation, 8-bit data is converted into high-level “1” bits at four bit positions of a bit pattern.
It shall be 15-bit data. In this case, when a low level “0” bit is inserted between the high level “1” bit and the high level “1” bit, two or more low level “0” bits are inserted, Two high-level "1" bits are present at each of the odd bit position and the even bit position. The 15th bit is always a low level “0” bit.

FIG. 2 shows an example of a reproducing apparatus for a magneto-optical disk in which 8-bit data is recorded by being subjected to 4/15 modulation as described above.

In the figure, (1) is a magneto-optical disk. The magneto-optical disk (1) has a track T as shown in FIG.
Are formed in a spiral shape, and data is recorded along the track T. The diameter of the magneto-optical disk (1) is, for example, 130 mm, and 20,000 tracks T are formed, for example. One track is divided into, for example, 32 sectors S, and data is recorded for each sector S. Sector S
Has a capacity of, for example, 512 bytes. Therefore, 1
16K bytes of data can be recorded on a track, and 320M bytes of data can be recorded on one magneto-optical disk.

The magneto-optical disk (1) is provided with a servo area SA corresponding to 2 bytes for every 16 bytes of data, as shown in FIG. Pit in servo area SA
P ₁ , P ₂ , and P ₃ are arranged, and a mirror section M is provided. Pits P ₁ and P ₂ are provided in order to perform the tracking control. In other words, the pits P ₁ and P ₂ are located disproportionately in opposite directions from the center of the track T. By reproduced signal of the pits P ₁ and pit P ₂ is controlled to be equal to each other, the laser beam is traced along the track T in the center between the pits P ₁ and the pit P _2, the tracking control is performed . Pit P ₃ is provided to form a reference signal. That, PL by using the output signal of the pit P ₃ to be reproduced in each servo area SA
L forms the reference signal. The mirror section M is provided for performing a focusing servo.

In FIG. 2, a magneto-optical disk (1) is rotated by a spindle motor (2). The rotation of the spindle motor (2) is controlled by a spindle servo circuit (3). Terminal (4) for spindle servo circuit (3)
The reference signal is supplied from the spindle servo circuit (3)
As a result, the magneto-optical disk (1) is rotated at a constant angular velocity.

On the magneto-optical disk (1), 8-bit data is recorded after being modulated by 4/15. The reproduction signal from the optical head (5) is supplied to an A / D converter (7) via a head amplifier (6), and also to a tracking servo circuit (8) and a focusing servo circuit (9). An output signal of the tracking servo circuit (8) is supplied to a horizontal feed mechanism of the optical head (5), and an output signal of the focusing servo circuit (9) is supplied to a vertical feed mechanism of the optical head (5). . Tracking servo circuit (8) is configured to control so as to use the reproduction signal of the pit P ₁ and P ₂ described above, the reproduced signal of the reproduced signal and the pit P ₂ of the pit P ₁ are equal. The focusing servo circuit (9) performs focusing servo using the reproduction signal of the mirror section M.

The reproduction signal is sampled corresponding to the bit position by the A / D converter (7) to be converted into a digital signal, and then supplied to the differential detection means (10). This differential detection means (10)
Compares the levels of the reproduced signals corresponding to the respective bit positions of the 15-bit data, and compares the levels of the reproduced signals at the odd-numbered bit positions with the two higher bit positions and at the even-bit position with the higher two bit positions. A high-level "1" bit is output correspondingly, and a low-level "0" bit is output corresponding to the other bit positions. Thus, the data recorded on the magneto-optical disk (1) is reproduced.

Also, differential detection means (10)
Is supplied to 14-8 conversion means (11) composed of, for example, a ROM, and demodulated by 4/15 modulation. In this case, since the fifteenth bit of the 15-bit data is always at the low level "0", the 14-8 conversion means (11) is sufficient. Then, the data returned to the 8-bit data by the 14-8 conversion means (11) is supplied to the error correction means (12), where the data is corrected for errors, and is then led out to the output terminal (13).

Such a reproducing apparatus is described, for example, in Japanese Patent Application No. 61-287221.

[Problems to be solved by the invention]

In the reproducing apparatus shown in FIG. 2, the differential detection means (10) compares the level of the reproduced signal corresponding to each bit position of the 15-bit data,
Since a high-level "1" bit is output preferentially at a high-level bit position, depending on the bit pattern of the 15-bit data recorded on the magneto-optical disk (1), the differential detection means may be used. (10) There is a possibility that incorrect data is output.

For example, as shown in FIG. 5A, the 15-bit data recorded on the magneto-optical disk (1) is “000001000011”.
When it is “100”, the level of the reproduced signal is changed as shown by the solid line in FIG. In this case, 6
The position is a high level "1" bit, but the 5 and 7 positions on both sides of the bit are low level "0". On the other hand, 10 positions are low-level "0" bits, while the following 11 to 13 positions are high-level "1" bits. Therefore, the level of the reproduced signal corresponding to 10 positions is higher than the level of the reproduced signal corresponding to 6 positions.

Therefore, this reproduced signal is converted by the A / D converter (7)
When the digital signal sampled and corresponding to the bit position shown in FIG. 9C is supplied to the differential detection means (10), the bit position having a higher level in the odd bit position and the even bit position is obtained. Are as shown in FIGS. 6A and 6B, respectively. From the output side, as shown in FIG. 5E, “00000000011110”
15-bit data of "0" is output. That is, the 6-position bit position is originally a high-level “1” bit but is a low-level “0” bit, and the 10-position bit position is a low-level “0” bit but is a high-level bit. This is a “1” bit.

The present invention has been made in consideration of such a point, and is intended to prevent erroneous data demodulation as described above.

[Means for solving the problem]

The present invention provides a data demodulation circuit that obtains 8-bit data from a reproduction signal of a recording medium on which 8-bit data is so-called 4 / 15-modulated and is modulated into 15-bit data. The level of the reproduction signal corresponding to each bit position of the data is detected, and the two bit positions from the higher level at the odd-numbered bit positions and the two bit positions from the higher level at the even-numbered bit positions correspond to the high level. A differential detection means (10) for outputting a bit of "1" and outputting a low-level "0" bit corresponding to the other bit positions, and 15 bits of the differential detection means (10). Conversion means (11) for converting data into 8-bit data;
Pattern detecting means (22) for detecting a pattern of "00" from the level of the reproduction signal corresponding to each bit position of the 15-bit data, and a differential based on the detection output of the pattern detecting means (22) The detection means (10) is controlled, and the bit positions corresponding to the pattern "00" are excluded from the two bit positions.

[Action]

In the above configuration, the pattern of "00" is detected by the pattern detecting means (22), and the bit position corresponding to the pattern of "00" is the high-level "1" bit in the differential detection means (10). Are excluded from the bit position to be output. Therefore, it is possible to satisfactorily prevent a low-level “0” bit from being output as a high-level “1” bit in the “00” pattern.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIG. 1, the same reference numerals are given to the corresponding parts in FIG. 2, and the detailed description thereof will be omitted.

In the A / D converter (7) of the present example, a reproduced signal having a frequency twice the sampling frequency in the example of FIG. 2 is sampled. That is, sampling is performed corresponding to the bit position, and also between the bit positions. The digital signal sampled at the bit position is supplied to the differential detection means (10) through the b side of the changeover switch (21) in the same manner as in the example of FIG. On the other hand, the digital signal sampled between the bit positions is supplied to the comparator (22) constituting the "00" pattern detecting means via the a side of the changeover switch (21). That is, the changeover switch (21) is alternately switched to the a side and the b side at the sampling frequency.

The output signal of the A / D converter (7) is supplied to a comparison level signal forming circuit (23). In the comparison level signal forming circuit (23), for example, an average value of the output signal of the A / D converter (7) is obtained, and the average value signal is directly or subjected to a predetermined gain adjustment to obtain the comparison level signal.
Eth is formed, and this comparison level signal Eth is supplied to the comparator (22)
Supplied to

In the comparator (22), the digital signal sampled between the bit positions by the A / D converter (7) is compared with the comparison level signal Eth, and the digital signal is output from the comparator (22). A signal SD having a high level “1” when it is larger and a low level “0” when it is small is output. In this case, when the signal SD goes to a low level "0", the bit pattern at the bit positions on both sides of the signal SD is "00".
The pattern "00" is detected.

The output signal SD of the comparator (22) is supplied to a differential detection means (10). In the differential detection means (10), the bit position corresponding to the pattern of "00" is shifted from the bit position for outputting the high-level "1" bit even when the level of the reproduction signal is high. Excluded. That is, the differential detection means (10) compares the level of the reproduction signal corresponding to each bit position of the 15-bit data, and determines the level at the two bit positions and the even bit position starting from the higher level at the odd bit position. Outputs a high-level “1” bit corresponding to the two bit positions from the higher bit, and a low-level “0” corresponding to the other bit positions.
Are output, but the bit position corresponding to the pattern “00” is excluded from the two bit positions.

The present example is configured as described above, and the reproduced signal is, for example, a signal whose level has changed as shown by a solid line in FIG. 5B, while the comparison level signal Eth is indicated by a dashed line in FIG. As shown. Therefore, while the reproduced signal is sampled by the A / D converter (7) corresponding to the bit position shown in FIG. D to be a digital signal, the output signal SD of the comparator (22) is As shown in FIG. That is, 1 and 2 position, 2 and 3 position, 3 and 4 position, 4 and 5 position, 7 and 8 position, 8 and 9 position, 9 and 10 position, 14 and 15 position are patterns of “00”. Is detected.

By the way, as described above, the order of the bit positions having higher levels in the odd bit position and the even bit position of the reproduction signal is as shown in FIGS. 6A and 6B, respectively.
Since the position is detected to be a pattern of “00”, the 10 positions are excluded from the bit positions for outputting the high-level “1” bits in the differential detection means (10). Then, instead, six positions are advanced.

Therefore, in this example, the differential detection means (10) outputs "00" as shown in FIG.
0001000011100 "is output. This is the same as the 15-bit data recorded on the magneto-optical disk (1) (see FIG. 1A).

Thus, according to the present example, the comparator (22) sets “0”
A "0" pattern is detected, and the differential detection means (10) outputs a high-level "1" bit at the bit position corresponding to the "00" pattern even if the level of the reproduction signal is high. In this case, the differential detection means (10) does not output erroneous data. Thereby, erroneous data demodulation can be prevented.

〔The invention's effect〕

According to the present invention described above, the pattern of “00” is detected from the level of the reproduction signal corresponding to each bit position of the 15-bit data, and the differential detection means corresponds to the pattern of “00”. Since such bit positions are excluded from the bit positions that output high-level “1” bits, erroneous data is not output, and erroneous data demodulation can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram of a main part of one embodiment of the present invention, FIG. 2 is a block diagram of a conventional example, FIG.
FIGS. 5 and 6 are diagrams for explaining the servo, and FIGS. 5 and 6 are diagrams for explaining the present invention. (1) is a magneto-optical disk, (5) is an optical head, (7)
Is an A / D converter, (10) is a differential detection means, and (11) is a 14-8 conversion means.

Claims (1)

(57) [Claims] 1. An 8-bit data having a low level "0" when a low level "0" bit is inserted between a high level "1" bit and a high level "1" bit. Two or more bits are inserted, and the high-level “1” bit is converted into 15-bit data that is present two at each of the odd bit position and the even bit position. In the data demodulation circuit for obtaining 8-bit data, the level of the reproduction signal corresponding to each bit position of the 15-bit data is detected, and the two bit positions and the even bit positions in the odd bit position from the higher level are detected. The differential detection outputs a high-level "1" bit corresponding to the two bit positions from the higher level and outputs a low-level "0" bit corresponding to the other bit positions. Conversion means for converting the 15-bit data from the differential detection means into 8-bit data; "00" from the level of the reproduction signal corresponding to each bit position of the 15-bit data. Pattern detection means for detecting the pattern of the pattern detection means, wherein the differential detection means is controlled based on the detection output of the pattern detection means,
A data demodulation circuit characterized in that a bit position corresponding to a pattern of "0" is excluded from the two bit positions.